1. Field of the Invention
The present invention relates to an exposing method, and more particularly to a production support system and operation and management technique of an exposure unit in semiconductor manufacturing.
2. Description of the Related Art
In recent years, as an exposure unit used in photolithography of semiconductors, an optical exposure unit of the scan exposing type which performs exposures by moving a reticle and a wafer in the direction reverse to each other to reduce the diameter of a projection lens (hereinafter referred to as a scan exposure unit) has been developed.
Exposing with a scan exposure unit causes errors called a lens distortion error, a stage matching error and so on.
A lens has a specific distortion called a lens distortion. With a lens distortion, the position of a pattern to be transfer shifts from the designed transfer position. If the shift is large, the product will be defective.
Two different exposure units have their own distortions. When overlaying patterns with different exposure units, it is necessary for exact overlaying to know relative distortions in combination of two exposure units.
When overlaying patterns with one same exposure unit, distortion is the same in an overlaying pattern and an overlaid pattern, and generally a relative shift does not occur. However, if an interval between the overlaying pattern exposing process and the overlaid pattern exposing process increases causing the error to change with time, a shift will occur between the two patterns. If this shift is large, the product will be defective.
When two exposure units are combined for overlaying patterns, a shift occurs between two patterns. Even if one exposure unit is used, a shift occurs between two patterns due to distortion changes with time. If this shift is large, the product will be defective.